Internal combustion engines have a cylinder block and at least one cylinder head which are connected to one another to form the cylinders of the engine. During the charge exchange, the combustion gases are discharged via the outlet openings and the charging of the cylinders takes place via the inlet openings. In order to control the charge exchange, an internal combustion engine requires control elements such as lifting valves and actuating devices for actuating the control elements. The valve actuating mechanism required for the movement of the valves, including the valves themselves, is referred to herein as the valve drive.
According to the prior art, the exhaust lines which adjoin the outlet openings of the cylinders are at least partially integrated into the cylinder head and are merged to form a single overall exhaust line or a plurality of overall exhaust lines. The merging of exhaust lines to form an overall exhaust line is referred to herein as an exhaust manifold.
Downstream of the at least one manifold, the exhaust gases are then commonly supplied to a turbine. For example, the turbine of an exhaust gas turbocharger, and if appropriate, are conducted through one or more exhaust gas after-treatment systems.
However, the inventors herein have recognized potential issues with such systems. As one example, according to the prior art, turbines are, in terms of the dimensioning, designed with a certain safety margin in order to avoid excessively high pressures in the inlet region. Taking a maximum expected exhaust gas mass flow at a particular pressure and temperature as a starting point, the turbine is designed with a flow cross section approximately 10% to 15% larger than is theoretically required, or would theoretically be necessary for the exhaust gas mass flow to be handled. The background to this measure is that the pressure in the inlet region of the turbine should not exceed a pre-definable admissible pressure. For example, if the actual exhaust gas mass flow exceeds the maximum expected exhaust gas mass flow in individual cases, and/or the exhaust gas pressure is temporarily and unexpectedly higher than the maximum expected exhaust gas pressure.
The exhaust gas pressure upstream of the at least one impeller must not become arbitrarily high, because it might otherwise be possible for an outlet valve to be opened counter to the spring force of the valve spring of the valve drive. This may result in the valve spring forcing the valve into the direction of the valve's closed position. Eliminating this risk by way of a stronger valve spring is not expedient, as this may increase the friction losses within the valve drive.
The provision of a safety margin in terms of the dimensioning yields numerous disadvantages. The larger turbine that may be used has a higher weight and may be more voluminous, giving rise to an increased space requirement. The at least one impeller may therefore be of correspondingly larger dimensions and have greater inertia. For this reason, the turbine exhibits a relatively poor response behavior. The main disadvantage, however, is the relatively poor efficiency of the relatively larger turbine which, during operation, is acted on primarily with exhaust gas mass flows smaller than the exhaust gas mass flows that could actually be handled. Such a turbine exhibits highly unsatisfactory operating behavior in the presence of small exhaust gas mass flows. It is here in particular that the large design of the turbine owing to the safety margin has a disadvantageous effect. In this way, it may be desirable to employ an internal combustion engine system having a turbine of a smaller size.
The above statements apply not only to turbines which have a fixed, non-variable geometry but also to turbines with variable turbine geometry. In the case of turbines of the latter type, the provision of a safety margin is allowed for such that the maximum expected exhaust gas mass flow at a particular pressure and a particular temperature is handled with an approximately 85% to 90% open flow cross section. To be able to counteract higher exhaust gas pressures than expected, or to be able to manage greater exhaust gas than expected, it is then possible for the variable turbine geometry to be adjusted further. That is to say, the flow cross section can be opened still further.
Against the background of that stated above, it is an object of the present subject matter to provide an internal combustion engine according to the preamble of claim 1, which is optimized with regard to the problem of an excessively high pressure in the inlet region of the turbine.
Said object may be achieved by means of an internal combustion engine comprising at least one turbine with a turbine housing in which there may be arranged at least one impeller which may be mounted on a rotatable shaft, in which internal combustion engine, the turbine housing has an inlet region for the supply of exhaust gas. The inlet region being arranged upstream of the at least one impeller and the outlet region, which belongs to an exhaust gas discharge system, being arranged downstream of the at least one impeller and adjoining the at least one impeller. At least one exhaust gas-conducting flow duct may be provided which connects the inlet region to the outlet region via the impeller, and wherein, at least one overpressure line may be provided which branches off from the at least one exhaust gas-conducting flow duct upstream of the outlet region and which opens into the exhaust gas discharge system downstream of the at least one impeller, wherein a self-controlling pressure valve may be arranged in the overpressure line.
According to the present subject matter, at least one overpressure line may be provided in the turbine housing. Each overpressure line may further be equipped with a self-controlling pressure valve which opens automatically when the pressure in the inlet region of the turbine exceeds a pre-definable pressure. This may serve to prevent excessively high pressures from prevailing in the inlet region.
As a result, it may no longer be necessary for the turbine to be designed with a certain safety margin in mind. That is to say, the turbine may no longer need to be designed to be larger than is realistically necessary for the exhaust gas mass flow to be handled safely. The omission of said safety margin-induced over-dimensioning may lead to a smaller turbine, which may then have a lower weight and may be less voluminous. The response behavior is likewise improved owing to the lower inertia of the rotor. Further, the efficiency of said smaller turbine may be higher, and in particular, the operating behavior in the presence of relatively small exhaust gas mass flows may considerably be improved.
In one example, the issues described above may be addressed by an internal combustion engine comprising at least one turbine with a turbine housing in which there is arranged at least one impeller which is mounted on a rotatable shaft, in which internal combustion engine, the turbine housing has an inlet region for the supply of exhaust gas, the inlet region being arranged upstream of the at least one impeller and the outlet region, which belongs to an exhaust gas discharge system, being arranged downstream of the at least one impeller and adjoining the at least one impeller, at least one exhaust gas conducting flow duct is provided which connects the inlet region to the outlet region via the impeller, wherein at least one overpressure line is provided which branches off from the at least one exhaust gas-conducting flow duct upstream of the outlet region and which opens into the exhaust gas discharge system downstream of the at least one impeller, wherein a self-controlling pressure valve is arranged in the overpressure line. In this way, it may no longer be necessary for the turbine to be designed with a certain safety margin. In other words, it may not be necessary to design the turbine to be larger than is necessary for the exhaust gas mass flow to be handled.
As one example, in the case of turbines with variable turbine geometry, the maximum expected exhaust gas mass flow of a particular pressure and a particular temperature is managed with the flow cross section fully open. In the presence of higher exhaust gas pressures, the geometry is not opened further, as it is already fully open. Rather, the overpressure valve automatically opens when the pressure in the inlet region of the turbine exceeds a pre-definable pressure. By doing this, the turbine pressure and the engine backpressure may boost the turbine speed automatically.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.